  .menu {
      width: 478px;
      height: 286px;
      margin: 50px auto;
      overflow: hidden;
      position: relative;
  }
  
  .pic {
      width: 478px;
      height: 268px;
  }
  
  .pic img {
      display: block;
      display: none;
  }
  
  .pic img:nth-child(1) {
      display: block;
  }
  
  .bt {
      width: 100%;
      height: 30px;
      position: absolute;
      bottom: -40px;
      left: 0px;
      background: rgba(51, 51, 51, 0.5);
      transition: all 0.3s ease 0.1s;
  }
  
  .bt span {
      width: 30px;
      height: 30px;
      float: left;
      display: block;
      background: #000;
      color: #FFF;
      text-align: center;
      line-height: 30px;
      border-radius: 50%;
      margin-right: 8px;
      cursor: pointer;
  }
  
  .bt .right {
      float: right;
  }
  
  .bt span.on {
      background: #F00;
  }